(i) Technical Field
The present invention relates to a surface emitting semiconductor laser, a surface emitting semiconductor laser device, an optical transmission device and an information processing apparatus.
(ii) Related Art
A surface emitting semiconductor laser, which is typically a vertical cavity surface emitting laser: VCSEL), is utilized as an optical source in a communication device and an image forming apparatus. The VCSEL used as the optical source is required to have improved optical output and electro static discharge (ESD) in the single transverse mode and to have lengthened life by reducing the resistance and heat radiation performance.
A typical selective oxidation type VCSEL has a current confining layer in which an oxide aperture formed by selective oxidation is formed within a vertical cavity structure. The oxide aperture has a function of confining current injected via an electrode and injecting high-density current in an active region. The oxide aperture has a further function of confining light generated in the active region in the center of emission due to the difference in refractive index between the outside of the oxide aperture and the inside thereof. The single transverse mode may be realized by reducing the diameter of the oxide aperture of the current confining layer to about 3 micron. As the oxide aperture diameter reduces, the resistance of the laser increases and the heat generation temperature rises, so that life may be shortened. Further, a reduced oxide aperture diameter results in a reduced optical output.
An increased cavity length may be a solution to realize higher optical output and longer life of VCSEL. A VCSEL having an increased cavity length has a cavity that may be typically defined by lengthening the cavity by 3 to 4 μm (approximately equal to ten to twenty times the oscillation wavelength). The increased cavity length increases the difference in optical loss between the primary transverse mode having a small divergence angle and a high-order transverse mode having a large divergence angle. Thus, the single transverse mode may be realized even using an increased oxide aperture diameter. In the VCSEL with the longer cavity, the oxide aperture diameter may be increased up to about 8 μm, and the optical output may be increased up to about 5 mW.